1.1 Field of the Invention
The exemplary, illustrative, technology herein relates to systems, software, and methods for detecting and excising radio-frequency noise, such as the spur and impulse types characteristic of man-made radio-frequency noise, within desired spectrum ranges and configuring dynamic spectrum access-enabled (DSA-enabled) systems to make efficient use of available spectrum despite this radio frequency noise. These techniques permit a DSA system to identify additional available spectrum that would otherwise be excluded from use with current detectors.
The technology herein has applications in the areas of mobile radio communications, dynamic spectrum re-use, and improved efficiency in the use of available radio spectrum. This invention is also applicable to other signal detection areas such as SIGINT.
1.2 The Related Art
Cellular phones, personal digital assistants, walkie-talkies, garage door openers, television remote controls, baby monitors, computers, wireless routers and other devices can all incorporate radio technology to establish and maintain communications using the electromagnetic frequency spectrum (hereinafter referred to simply as “spectrum”). Due to the limited nature of spectrum, and the number of potential and actual uses for it, regulatory agencies have been empowered to determine allocations of spectrum for various uses and/or users. This is typically done by allocating a range of frequencies, or a “band”, to a given use and/or users, and prohibiting interference in that band from other uses or users. Frequency bands may be further subdivided into channels, each of which represents a range of frequencies that may be used.
Some radio frequency (RF) devices, such as cordless telephones, can automatically choose a channel from among those channels assigned for use by the device in order to establish and maintain communications and then cease use of the channel when the radio session is finished. They may do this to avoid use of channels currently in use by other devices, or they may randomly choose channels from their available set of frequencies as a very limited form of security. However, such devices are unable to automatically adapt to significant or challenging changes within the network or spectrum environment. They simply select a channel from a limited set of predefined channels within an allocated band. Networked radios and other devices designed to operate within one particular channel, or set of channels, cannot operate outside of the designated channels without appropriate authorization from regulatory authorities or spectrum owners and/or modification of the radios. For example, a radio may search a specified band to find an open channel for communications with the network. The radio will sequentially or randomly step or hop through the band until an open channel is found or an indication is given (e.g., through a control signal) that the network is busy (e.g., no channels are available). Such a radio, however, does not determine a new band or frequency range from which to search for channels if a channel is not found. Rather, the radio either works within its prescribed frequency band according to its fixed characteristics (such as transmit power, bandwidth, and modulation scheme).
If a typical radio confronts interference from other devices or natural effects, such as power line arcing or lightning, its communications signals may not be transmitted or received while the interference persists. A typical radio communication system, however, is not able to adjust its own operation to overcome, and typically cannot independently determine how to overcome, problems such as harmful interference that may prevent the functioning of the system, or degrade, obstruct, or repeatedly interrupt service.
Dynamic spectrum access-enabled (DSA-enabled) devices are useful for dealing with these problems. The portions of spectrum available for use and actually used by a DSA-enabled device or network can be defined by a combination of the spectrum selected by an operator of the device or network, the spectrum in which the DSA-enabled devices are capable of operating, and access limitations set by policy, regulatory, service provider, and other requirements. Through their ability to adjust spectrum use based on existing conditions and other factors, DSA-enabled devices can avoid interference by shifting communications to parts of the spectrum where interference is absent, or avoid the use of spectrum where the DSA-enabled device's operations would create interference for others.
Some DSA-enabled devices detect and classify signals based upon identified and pre-specified signal characteristics. Signal noise may interfere with signal detection and identification. For example, energy-based signal detectors may discern noise as non-cooperative device signals since their energy level passes a threshold level test and then disqualify the affected channels as “in-use”, even when the channels are not actually used. When noise occurs frequently enough, even noise discrimination methods that include signal duration factors in their detection methods will identify available spectrum as in use due to the noise.
Furthermore, conventional noise elimination techniques typically use such methods such as averaging signal strengths. These can be ineffective for eliminating some classes of noise. The variance of certain types of noise energy can be large compared to noise floor energy and may be similar in strength to signal energy. Averaging signal strengths doesn't reduce this noise energy relative to signal energy. Methods for reducing the noise level relative to the signal level are needed in order to reduce “false positive” signal detections caused by noise.
In urban environments, where man-made noise-creating devices are typically present in large numbers and at high densities, man-made noise may be present in such quantity as to make DSA channel selection difficult or even impossible. For example, experiments in New York City showed that many channels were affected by man-made noise (“Evaluation of the Performance of Prototype TV-Band White Space Devices”, FCC Report, ET Docket No. 04-186, 2008). Man-made noise is often produced at high power levels, which means that the man-made noise may have larger received amplitude than the non-cooperative device signals which the DSA system must avoid interfering with to comply with regulatory requirements or for other reasons. The high power man-made noise can cause DSA systems to unnecessarily abandon channels that are not actually being used by non-cooperative devices. This leads to inefficient spectrum use, and in some cases can prevent a DSA-enabled device from operating at all. What is needed is a way to ignore man-made noise in automated ways and to permit auto-configuration of DSA-enabled systems to use more channels that are not being used by non-cooperative devices. This would have the effect of making more spectrum available for use. Avoiding false non-cooperative signal detections (“false positives”) caused by man-made noise involves new detection mechanisms and classification mechanisms that operate in both the time and frequency domains.
Some techniques involve collection of historical signal information and analysis of the collected signal data over time in an effort to determine noise patterns. These techniques may be less effective when the DSA-enabled radio is mobile, due to the often localized and transient nature of certain noise types, such as man-made noise. These techniques are also less effective when the occurrences of noise are infrequent, or do not possess a predictable pattern.
Reliable methods for detecting and classifying spur and impulse noise, and enabling DSA-enabled devices to make use of the spectrum in which these types of noise occur, without treating the affected channels as “in-use,” are needed. DSA-enabled devices using such methods could be effective within urban environments where existing DSA-enabled devices may not be reliably usable. Impulse and spur noise detection methods provide an opportunity for making significant spectrum available for DSA-enabled device use that is currently being treated as unusable.